As generally understood, an internal combustion engine, for example, operates over a narrow range of speeds. Accordingly, a transmission is typically provided between the engine and an implement, such as a vehicle wheel or the bucket of an earth moving machine, so a wide range of torques can be applied to the implement. Many current transmissions, as well as earlier ones, include a series of gears, whereby one or more gears within the transmission are selected depending on load conditions. For example, as a vehicle initially accelerates, the engine speed is increased and the transmission selects a higher gear ratio (the ratio between the engine speed to wheel speed) which delivers a higher torque to the wheels. As the vehicle speed approaches a desired speed and less torque is required, the transmission shifts to a lower gear ratio.
Automatic transmissions are known which do not require manual selection of transmission gears. Typically, automatic transmissions include a torque converter, which selectively allows the engine to run independently of the transmission. If the engine is running at a slow speed, the amount of torque passed through the torque converter to the implement is relatively small. When the engine speed increases, however, more torque is transmitted to the implement. Accordingly, operators of machines having automatic transmission are accustomed to hearing the engine speed increase when additional output power or torque is required to be applied against a load.
More recently, however, so-called continuously variable transmissions (“CVTs”) have become commercially available which continuously adjust the gear ratio, so that the engine maintains an optimal speed regardless of the load. One such CVT is described in U.S. Pat. No. 4,916,900.
Machines having a CVT typically do not have a torque converter, and the engine in such machines can remain at a substantially constant speed while the torque applied to the implement is varied. Thus, although CVTs can improve fuel economy, the operator of such machines typically does not hear the engine rev or feel machine vibrations, as would be expected when greater torque is required to act against an increased load. The operator may then attempt to overcompensate for the apparent lack of engine power, even though such overcompensation is not necessary and could be detrimental.
In addition, with load sensing hydraulics and improved transmissions, the cabs of earthmoving machines have become quieter such that operators may lose noise feedback that they would otherwise rely on to gauge the amount of force delivered by the machine.
The present disclosure is directed to overcome one or more of the shortcomings in the prior art.